Cretaceous Exhumation of Proterozoic Carbonatite on the Northern Margin of the North China Craton Constrained by Apatite Fission-Track and (U-Th)/He Geochronology

AbstractSome carbonatites related to Proterozoic rift activities developed on the northern margin of the North China Craton and have a close genetic relationship with certain types of mineralization. We obtained new fission-track and (U-Th)/He geochronological data from fragments of pegmatitic apatite that coexists with Proterozoic igneous carbonatite along the border of three provinces (Hebei, Shanxi, and Inner Mongolia). Twenty fragments yielded a fission-track central age of 124.1 ± 6.5 Ma (1σ). Thermal-history inversion and track-length distribution suggest rapid Early Cretaceous cooling through the apatite partial-annealing zone. Sixteen single-fragment apatite (U-Th)/He ages range between 82.2 ± 1.8 and 109.6 ± 2.3 Ma, with the age variation much larger than the analytical uncertainty. Several reasons could account for this dispersion. While alpha-particle redistribution resulted from U and Th inhomogeneties, chemical variations and radiation damage are the most probable causes. We calculated the me...